Chapter 8Chapter 8

The Nervous System

Organization of nervous Organization of nervous systemsystem

Central Nervous SystemCentral Nervous System

Peripheral Nervous Peripheral Nervous SystemSystem

Integration of CNS and PNSIntegration of CNS and PNS

The Neuron is theThe Neuron is the

Functional unit of the nervous systemFunctional unit of the nervous system

The “model” neuron

Peripheral Nervous SystemPeripheral Nervous System

Afferent NeuronsAfferent Neurons

Sensory Receptors send information to Sensory Receptors send information to CNSCNS

Efferent NeuronsEfferent Neurons Carry information to effector cells of the bodyCarry information to effector cells of the body

PNS is divided intoPNS is divided into

1. Autonomic Division1. Autonomic Division

– Sympathetic branchSympathetic branch

– Parasysmpathetic branchParasysmpathetic branch

PNS is divided intoPNS is divided into

2. 2. Somatic Motor divisionSomatic Motor division

– Controls skeletal muscleControls skeletal muscle

PNS divided into PNS divided into

3. Enteric division3. Enteric division

Glial cells of the PNSGlial cells of the PNS

Schwann CellsSchwann Cells Satellite CellsSatellite Cells

The PNS and Schwann CellThe PNS and Schwann Cell

Nodes of Ranvier: Are not Nodes of Ranvier: Are not covered by myelincovered by myelin

Central Nervous SystemCentral Nervous System

Glial cells of CNSGlial cells of CNS

AstrocytesAstrocytes– NutritionNutrition

EpendymalEpendymal– barrierbarrier

MicrogiliaMicrogilia– ImmuneImmune

OligodendrocyteOligodendrocytess– MyelinMyelin

An overview of glial cellsAn overview of glial cells

Remember the neuron… Remember the neuron…

Communicates information Communicates information throughout the body, but how?throughout the body, but how?

Another picture of vertebrate Another picture of vertebrate neuronneuron

By Action Potentials!By Action Potentials!

Action Potentials Action Potentials areare our our nerve impulses. nerve impulses.

It’s all to do with communication.

We can look at an action We can look at an action potential as an electrical potential as an electrical

event.event.

First we remember First we remember howhow ions ions influence the membrane influence the membrane potential (Em) of a cell.potential (Em) of a cell.

K+

Large non-diffusible anionic proteins

Is the charge across this cell zero?

K+

Chemical gradient

Electrical Force

Permeable only to K+

Volt meter

No! No!

It is –90 mV! Why?It is –90 mV! Why?

Now let’s try to think about a Now let’s try to think about a living excitable cell…living excitable cell…

Resting Neuron Membrane Resting Neuron Membrane PotentialPotential

Volt meter

Now what does the volt meter read?

-70 mV at rest -70 mV at rest butbut the Em the Em can change when a nerve is can change when a nerve is

“excited”.“excited”.

But why do we care about But why do we care about these values?these values?

A change in Em results in NT A change in Em results in NT release!release!

But But howhow does this change does this change in charge occur so that the in charge occur so that the neurotransmitter neurotransmitter cancan be be

released?released?

A simple flow chart of electrical A simple flow chart of electrical eventsevents

Graded potentialsGraded potentials

Action potentialsAction potentials

Neurotransmitter releaseNeurotransmitter release

Graded potentials decrease in Graded potentials decrease in strength as they spread out from the strength as they spread out from the

point of originpoint of originbut may bring about an action but may bring about an action

potential.potential.

The end of Part 1